Authors

Abstract

In the present work, three-dimensional direct numerical simulation (DNS) of n-heptane/air premixed combustionin turbulent boundary layer was performed to explore the near-wall ignition process with low-temperature chemistry. A reduced chemical mechanism with 58 species and 387 elementary reactions for n-heptane combustionwas used in the DNS. The general characteristics of the ignition process near the wall were examined. It wasfound that low-temperature ignition (LTI) dominates the upstream region, and high-temperature ignition (HTI)appears in the downstream region. The ignition process and the low-temperature chemistry pathways of the DNSare compared with those of a corresponding laminar case. It was found that the ignition process was affectedby turbulence, which results in thickened reaction zones. However, the carbon flow analysis of low-temperaturechemistry showed that turbulence rarely affects the low-temperature chemistry pathway. The combustion modesof various regions were scrutinized based on the budget terms of species transport equations and the chemical explosion mode analysis (CEMA). It was shown that the reaction term of RO2 is significant during the LTI processof the upstream region, and the reaction terms of CH2O and CO2 are evident in the downstream region, indicatingthe occurrence of HTI. It was also shown that auto-ignition is dominant in the upstream region. With increasingstreamwise distance, the contribution of flame propagation increases, which takes over that of auto-ignition in thenear-wall region